v='oooo';sed -n '/^\[aaaa\]/{p;:a;n;H;/^\[bbbb]/!ba;x;s/.*/'"$v"'/;G;};p'

line1=[aaaa]
content
line2=[bbbb]

let "0000" repalce the content.

替换两行之间的内容 replace content between two line

Bash